An integrated circuit (IC) is a semiconductor device containing many small, interconnected components such as diodes, transistors, resistors, and capacitors. These components function together to enable the IC to perform a task, such as control an electronic device or perform logic operations. ICs are found in computers, calculators, cellular telephones, and many other electronic devices.
ICs and other semiconductor devices are fabricated on small rectangles, known as “dies,” which are filled with multiple layers of the components, such as transistors, resistors, and capacitors, during the fabrication process. The connections between the layers are known as vias. A via is a metal interconnect coupled between two planar conductive layers in a semiconductor die. Multiple vias may be coupled together in what may be referred to as a “via chain” connecting one conductive region in an IC to another conductive region.
A manufacturing error in one of the components mentioned above may render an IC or semiconductor device incapable of functioning properly. For example, consider a memory device containing several ICs. If a transistor within one of the ICs fails to function properly, the memory device may produce memory errors. Vias are also subject to manufacturing errors. When a manufacturing error occurs in a via, the via may not conduct properly and thus may prohibit an IC from functioning correctly. For instance, an open via or a partially open via may prohibit a device from functioning as designed. An open via may have a high or infinite resistance, and a partially open via may have a higher than average resistance.
Vias in a semiconductor device may be tested by measuring the resistance of via test chains. This technique identifies via chains containing open vias and some partially open vias by their high resistance. A problem with this approach is that tests may fail to identify via chains containing vias that have slightly larger than expected resistances. Consider a via chain in which each via has an expected resistance. For example, a via may have an average resistance of between eight and twelve ohms. Thus, a via chain having one thousand vias has an expected resistance of between eight thousand and twelve thousand ohms. However, one via in the via chain could have a resistance of one thousand ohms, while the other vias have an average resistance of nine ohms. Thus, the resistance of the entire via chain is approximately ten thousand ohms. Even though one via is a partially open via, the resistance of the entire via chain may still fall within the expected resistance range. As a result, measuring the resistance of the entire via chain may fail to identify one or more vias with a higher than average resistance in the via chain.
Circuitry to test IC components on a semiconductor device, such as resistors, transistors, vias, and oscillators, may interface with an external testing device. While the test circuitry may test vias and other semiconductor device components so that flawed components may be identified, the test circuitry may take up space on or around the semiconductor device that may otherwise be used to fabricate more IC components. Thus, an apparatus and method that both accurately tests semiconductor devices and takes up little space on or around the semiconductor die would be beneficial.